Utilization of radio resources and channels is continuously subject to much research and development in order to optimize system throughput despite the limited availability of radio resources in communications systems. This is especially true when introducing new communications services to the exiting communications systems. An example of such new communications service is Multimedia Broadcast Multicast Service (MBMS). The benefit of this MBMS service is that it enables simultaneous distribution of data to several users using the same physical channel, i.e. so-called point-to-multipoint transmission. For more information of MBMS reference is made to the 3GPP document [1].
In order to reach bit rates that are high enough to provide video streaming over MBMS, in particular at or close to the cell borders, in existing GMS (Global System for Mobile communications) and EDGE (Enhanced Data rates for Global Evolution) communications system, it is expected that it will be necessary to use at least four time slots. However, as is well known to the person skilled in the art, the mobile units also have to listen to control channels, e.g. Broadcast Control Channel (BCCH), and perform radio quality measurements, including neighbor cell measurements during the MBMS communications session. This means that due to the multi-slot requirements of MBMS taken together with the control channel listening and quality measurements, the mobile units may have no available communications resources, i.e. time slots, for performing other temporary resource-demanding communications operations during the MBMS session.
For example, assume that a user of a mobile unit that is involved in a MBMS session in the form of receiving video data from a football match or a live TV show. The user might then want to transmit a message, e.g. SMS (Short Messaging Service), MMS (Multimedia Messaging Service) or e-mail message, or initiate a WAP (Wireless Application Protocol) interaction during the MBMS session. The mobile unit typically cannot perform such message transmission or WAP interaction without interrupting the MBMS session, with the result of missed radio blocks for the MBMS session. This is due to that the message transmission or WAP interaction will be performed by the mobile unit on one or more radio channels on which MBMS data will be transmitted.
The missed block reception is in particular a major problem, where the MBMS server typically has one common radio block queue for all (four) time slots and schedule the transmissions on a first-in-first-out basis. This means that a mobile unit that temporarily does not listen to a particular time slot is likely to miss radio blocks belonging to many different LLC (Logical Link Control) blocks. As a result, the throughput on the LLC layer and higher layers will be very low for the MBMS service.